Electric frequency responsive device



March 19, 1968 w. J. FITZGERALD ETAL 3,374,432

ELECTRIC FREQUENCY RESPONSIVE DEVICE Filed Jan. 24, 1966 INVENTORS William J. FLtzg cralcL Raoul A. For-est Jr. Co H J lac'carl no AGENT United Statcs Patent Ofiice 3,374,432 Patented Mar. 19, 1968 3,374,432 ELECTRIC FREQUENCY RESPONSIVE DEVICE William J. Fitzgerald, West Haven, and Raoul A. Forest,

IL, and CarlJ. Iaccarino, New Haven, Conn., assignors to J-B-T Instruments, Inc., New Haven, Comm, a corporation of Connecticut Filed Jan. 24, 1966, Ser. No. 522,501

7 Claims. (Cl. 32480) This invention relates to electric devices which respond to the frequency of an applied voltage.

The embodiment illustrated comprises a reed-type frequency meter, but the scope of the invention is determined by the appended claims and not by the specific disclosure of the specification.

Objects of the invention are to provide an improved frequency-responsive device having movable members of different resonant frequencies, wherein a more uniform response and deflection of the members is had over the intended range of frequencies; to provide a device of this type which is extremely simple, in expensive to manufacture, reliable and foolproof in operation, adaptable to a wide range of frequencies, small and compact, and which requires but simple and well-known fabricating techniques.

Another object is to provide, in a frequency responsive device, an improved field structure providing a graduated air gap and flux density, in conjunction with movable members of different resonant frequencies.

Other features and advantages will hereinafter appear.

In the drawings:

FIG. 1 is a front elevational view of a vibrating-reed type instrument embodying the invention.

FIG. 2 is a side elevation view of the instrument of FIG. 1.

FIG. 3 is a bottom plan view of the instrument.

Considering first FIG. 2, the instrument movement comprises a flat base plate which is constituted of magnetic material such as iron, soft steel, or the like, said base plate comprising the yoke portion of the magnetic circuit of the instrument.

On the base plate 10 there are mounted post assemblages 12 and 14 of magnetic material, the assemblage 14 including a cylindrical parmanent magnet 16. The assemblage 12 comprises a short cylindrical piece 18 through which a screw 22 passes. The assemblage 14 comprises in addition to the permanent magnet 16, a short cylindrical piece 24 which is secured in end-to-end relation to the magnet 16 by a screw 28.

Dial supporting posts 30, 32 are provided, having threaded bores to receive the ends of the screws 22, 28 respectively and the assemblages 12, 14 are shown as carrying a bobbin or coil form comprising end plates 34, 36 between which there is disposed a Winding or coil 38. As seen in FIG. 1, the coil 38 is of the air core type, having an elongate or slot shaped central opening or air core 40.

Secured under the dial supporting posts 30, 32 are elongate sheet metal pole pieces 42, 44 arranged to extend along opposite sides of the slot 40 constituting the air core of the coil 38. The pole pieces 42, 44 are additionally secured to the end plate 34 of the coil bobbin by small rivets 46 as seen in FIG. 1, and have roughly a triangular shape with the longest edge or hypotenuse nearest the reeds 48.

The above arrangement comprises a gap-type magnetic circuit wherein the pole piece 44 at the gap has, for instance a north polarity and the pole piece 42 at the gap a south polarity, following the designations given to the cylindrical magnet 16 in FIG. 2. The magnetic circuit includes the post parts 18 and 24 together with the yoke plate 10 and the permanent magnet 16, as well as the pole pieces 42, 44.

Mounted to extend through the air core 40 of the instrument is a plurality of vibratable reeds 48, carried on a block 49 which is secured to the yoke plate 10 in any desired manner. The reeds 48 are magnetic and preferably of identical length, but have different periods of vibration by virtue of the flag portions 50 thereof having different masses. For example, small amounts of solder may be placed on the undersides of the flags 50, and the excess filed away to provide the desired frequency response of each reed. In the present instance, the set of reeds 48 may start with a frequency of 56 and progress to a frequency of 64, in steps of one. A total of nine reeds would thus be evolved.

In accordance with the present invention there is provided a novel air gap of graduated magnetic flux density, effected by shaping the pole pieces 42, 44 whereby reeds at one end of the set 48 will be disposed in a greater flux density than reeds at the other end of the set. The low frequency reeds which have the heavier flags are arranged to be subjected to the smaller flux, and the higher frequency reeds which are lighter and have less mass or solder on their flags (and which require stronger forces to effect actuation through the same are as the lowerfrequency reeds) are subjected to the greater flux density. In consequence, there is obtained a desirable unformity of response of the reeds whereby the magnitude of movement and bandwidth of each reed is substantially equal.

As shown, the pole pieces 42, 44 have forwardly extended flanges 52, 54 respectively, said flanges being of tapered shape as viewed from the top or bottom of the instrument and also being angularly disposed with respect to each other and with respect to the plane of the reeds 48. This is effected even though the blanks from which the pole pieces 42, 44 are made, are identical. For, by folding the flanges 52, 54 along fold lines which are not parallel with the edges of the flanges, i.e., the hypotenuses of the blanks, there will be effected a tapered shape of flange and also a spacing between the flanges and the reeds, which varies or becomes less as the flanges are traversed from left to right, considering FIG. 1. In this figure, the leftmost reed of the set 48, designated by the numeral 58, will have the lowest frequency, say for example 56 cycles per second. This reed, which is heavier than the other reeds and slower, will be subjected to a lesser flux density by virtue of the pole flanges 52, 54 having at this location a greater spacing and also a greater front-to-rear dimension (at the left side of the movement of FIG. 1).

The front-to-rear dimension or depth of the flanges 52, 54 at the right side of FIG. 1 may be on the order of 4;- inch, and the front-to-rear dimension or depth at the left side of FIG. 1 may be A-inch. This means that the flanges are twice as deep at the left end, as compared to the right end. The spacing between the flanges at the right side may be on the order of of an inch, whereas the spacing at the left side may be or of an inch. Thus, the depth is double at the left side, and the spacing between the flanges is slightly less than double. The reluctance of the air gap, which varies directly with the spacing of the pole pieces and inversely with the cross-sectional area of the pole pieces, may be less at the left side of FIG. 1, resulting in a slightly greater total flux. But the flux density at the left side will be considerably less, because the slightly greater total flux will be spread over a polar area which is twice as large as that existing at the right side. We have found that with the structure as above provided, this lesser flux density will provide a lesser magnetism for the easierto-vibrate low frequency reed 58, and will result in a lesser force being exerted on such low frequency reed. In consequence there is obtained a more uniform response of the reeds, in spite of their different frequencies and different weights or masses at the flag portions, whereby the deflections can be substantially or more nearly the same. As

understood at present, the appreciably lesser flux density at the lower frequency reeds accomplishes this desirable result.

While we have illustrated one construction by which a lesser flux density is obtained at the left side, using a graduated style air gap, it will be understood that other structures are possible to obtain the same result.

However, the present construction achieves the graduated fiux density by the use of identical blanks for the two pole pieces, and by bending the pole flanges along fold lines which are angularly disposed with respect to the long edges or hypotenuses of the blanks. The greater area of the pole pieces at the left side is accompanied by a greater spacing of the same, the increase in spacing being shown as somewhat less than the increase in cross section. The net effect provides a lesser flux density, as already explained. This result is thus achieved with extremely simple pole pieces which are made from identical blanks, and are fabricated in a unique manner to provide the desired result.

Variations and modifications may be made within the scope of the claims, and portions of the improvements may be used without others.

We claim:

1. An electric frequency responsive device comprising, in combination:

(a) a plurality of juxtaposed magnetic members having difiTerent resonant frequencies,

(b) a winding disposed adjacent said members, to infiuence the same with a common magnetic flux when the winding carries current, and

(c) means including a magnetic field structure having pole pieces adjacent said members, for influencing the members with magnetic flux,

(d) said means providing a lesser flux density at a member having a lower resonant frequency than at a member of higher resonant frequency, thereby to render more uniform the response of the members to flux from said winding.

2. An electric frequency responsive device as in claim 1, wherein:

(a) the field structure comprises pole pieces on opposite sides of the members,

(b) those polar areas of the pole pieces which provide fiux for a member of lower resonant frequency being larger and providing a flux path of greater cross section than the areas providing flux for a member of a higher resonant frequency.

3. An electric frequency responsive device as in claim 2, wherein:

(a) said larger polar areas are spaced apart a greater distance than the areas providing flux for a member of higher resonant frequency.

4. An electric frequency responsive device as in claim 2, wherein:

(a) the magnetic members comprise flat strips disposed broadside to said polar areas.

5. An electric frequency responsive device as in claim 2:, wherein:

(a) the magnetic members are disposed in a row,

(b) the polar areas of said pole pieces being of tapered shape, extending on opposite sides of the row, and having their wider portions disposed at the member of lower resonant frequency.

6. An electric frequency responsive device as in claim 5, wherein:

(a) the pole pieces comprise sheet metal stampings having flanges constituting said polar areas.

7. An electric frequency responsive device as in claim 3, wherein:

(a) the pole pieces comprise sheet metal stampings formed from blanks of identical roughly triangular shape each with one long substantially straight edge,

(b) said stampings having tapered flanges folded at right angles and constituting said polar areas,

(c) the fold lines for said flanges being angularly disposed with respect to the long straight edges of the blanks.

References Cited UNITED STATES PATENTS 2,958,040 10/1960 Daschke et a1. 335-221 XR 3,079,555 2/1963 Daschke 324-80 BERNARD A. GILHEANY, Primary Examiner.

G. HARRIS, Assistant Examiner. 

1. AN ELECTRIC FREQUENCY RESPONSIVE DEVICE COMPRISING, IN COMBINATION: (A) A PLURALITY OF JUXTAPOSED MAGNETIC MEMBERS HAVING DIFFERENT RESONANT FREQUENCIES, (B) A WINDING DISPOSED ADJACENT SAID MEMBERS, TO INFLUENCE THE SAME WITH A COMMON MAGNETIC FLUX WHEN THE WINDING CARRIES CURRENT, AND (C) MEANS INCLUDING A MAGNETIC FIELD STRUCTURE HAVING POLE PIECES ADJACENT SAID MEMBERS, FOR INFLUENCING THE MEMBERS WITH MAGNETIC FLUX, (D) SAID MEANS PROVIDING A LESSER FLUX DENSITY AT A MEMBER HAVING A LOWER RESONANT FREQUENCY THAN AT A MEMBER OF HIGHER RESONANT FREQUENCY, THEREBY TO RENDER MORE UNIFORM THE RESPONSE OF THE MEMBERS TO FLUX FROM SAID WINDING. 